Some might conclude that there really are three Churches: the Church Militant, the Church Suffering, and the Church Triumphant. That is not the case at all any more than the Triune God – Father, Son, and Holy Spirit – are three distinct Gods. No, there is one God in three Persons. There is also one Church consisting of three parts. This is not to say that the three parts of the Church reflect or correspond to the three divine Persons, but there are some general similarities.
First, God is one in three divine Persons. As one translation of the Preface of the Holy Trinity puts it: ‘For with your Only Begotten Son and the Holy Spirit you are one God, one Lord: not in the unity of a single person, but in a Trinity of one substance. For what you have revealed to us of your glory we believe equally of your Son and of the Holy Spirit, so that, in the confessing of the true and eternal Godhead, you might be adored in what is proper to each Person, their unity in substance, and their equality in majesty.’ The Church is also one. The oneness does not come about by being collocated or by being exactly the same. No, the oneness of the Church is an expression of being in communion with one another. Thus, someone in a state of grace in the Church Militant is in communion with the entirety of the Church Suffering and of the Church Triumphant as well as being united to all of the other members of the Church Militant who are also in a state of grace. This union transcends time and space, culture and language, and every other quality that tends to divide us.
Unquestionably, the three Persons of the Holy Trinity are, as their title suggests, holy. The Father and the Son and the Holy Spirit are uniquely holy in a way that cannot be described nor can it be ascribed to anything or anyone other than the Trinity. The Church is also holy. But the holiness of the Church is not by nature as it is with God but by grace. The holiness of each member of the Church varies such that we can generally say that the members of the Church Suffering are holier than those of the Church Militant while those members of the Church Triumphant have obtained their full capacity for holiness. If we understand holiness to be closeness to God, then it becomes more clear how each part of the Church tends to vary in holiness: in this world we often struggle for holiness and sometimes fall, in Purgatory souls are infallibly and inexorably growing in holiness by shedding worldliness and all other things unworthy of heaven, and the souls in heaven enjoy the fullness of human holiness.
Another aspect of God is His omnipresence. He is everywhere in the created world and He exists outside and apart from what He has created. He is universal. So is the Church. Another word for universal is catholic, which is not a name or a title, but a true description of the Church. The word catholic is derived from the Greek word for universal: katholikos. Jesus clearly intended the Church to be universal since He made a point of saying “Go, therefore, and make disciples of all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Spirit, teaching them to observe all that I have commanded you. And behold, I am with you always, until the end of the age” (Mt 28:19-20). The universality of the Church extends to all of the nations, not just some, and until the end of time, not just for a few decades or centuries.
That catholicity, that universality, extends from Jesus Himself until this world ceases to be. From the Great Commission quoted above, it is clear that Jesus intended for the Apostles and their various successors to be the agents of that universality. From the Apostles we have Jesus’ teachings. From the Apostles we have a direct line back to Jesus’ own ministry, suffering, death, and resurrection. We also have from the Apostles the teaching authority entrusted to the Church: “He who hears you hears me, and he who rejects you rejects me, and he who rejects me rejects him who sent me… Amen, amen, I say to you, whoever receives the one I send receives me, and whoever receives me receives the one who sent me” (Lk 10:16, Jn 13:20). In other words, access to the Father is mediated through the Son by the ministry of the ones Jesus sent, and another word for one who is sent is apostle.
What this all means is that the Church is not only made up of three parts but has four essential and unmistakable marks: it is one, holy, Catholic, and apostolic.